There are many industrial operations which require processing of solid workpieces by material removal to cut, shape or clean the workpiece. It is already known, and commonly used in industry, to utilize high pressure, high velocity liquid jets for such material removal operations. These known methods and apparatus have achieved a high state of development but still leave much to be desired in respect to efficiency of material removal and residual effects on the workpiece and on the work site.
In the prior art, solid workpieces of hard material are cut by use of high velocity liquid jets which effect the cut by material removal in particulate form from the kerf. In some applications, an abrasive material is added to the jet stream to enhance the cutting action. Water and other liquids have been proposed for use in the formation of the jet stream. This cutting technique has been proposed for application to cutting of metal workpieces including exotic metals which are extremely hard. It has also been proposed for use in cutting composite materials, concrete and stone.
It has been a common practice to clean the surfaces by the use of sand blasting and the use of water blasting with entrained abrasive particles, for example in the removal of unwanted deposits on the exterior walls of buildings of brick and stone. This method of material removal typically leaves a very large amount of residue of the working fluid.
The prior art methods and apparatus for material removal as discussed above, are inefficient, produce a low rate of material removal and leave an unduly large amount of residue and waste at the work site. There is a need to overcome such disadvantages in a wide variety of industrial applications. A particular application, for example, is stone cutting in quarrying operations. In such operations, such as the mining of granite blocks, the cutting operation has to be performed in a relatively confined area wherein the cutting tool has to be manually supervised and controlled or sometimes manually manipulated. In such an operation, huge blocks of granite weighing many tons, for example, are cut in rectangular form from a monolith of great extent. It is desirable to sever the block with a narrow kerf and thereby minimize the amount of material removal required. It is also desirable to minimize the contamination of the air in the work area and to leave only a minimum amount of harmless residue.
The following patents relate to methods and apparatus for material removal by use of the high velocity jet stream of liquid or other material: U.S. Pat. No. 2,985,050 Schwacha, issued May 23, 1961; U.S. Pat. No. 3,746,256 Hall et al, issued Jul. 17, 1973; U.S. Pat. No. 4,594,924 Windisch, issued Jun. 17, 1986; U.S. Pat. No. 4,686,877 Jaritz et al, issued Aug. 18, 1987; U.S. Pat. No. 4,693,153 Wainwright et al, issued Sep. 15, 1987; and U.S. Pat. No. 4,723,387 Krasnoff, issued Feb. 9, 1988.
It is known in the prior art to use carbon dioxide in solid phase for use in cleaning a workpiece. In this prior art solid pellets of carbon dioxide are formed on the surface of a drum which is rotated at high speed to throw the pellets by centrifugal force against a workpiece for cleaning or other purposes.
The following patents relate to the use of cryogenic fluids in connection with cutting apparatus or methods. The Lightstone et al U.S. Pat. No,. 3,979,981, issued Sep. 14, 1976 discloses a method for shearing metal in which the metal is cooled to a cryogenic temperature and using shearing operations such as slitting, punching, and blanking. The Lightstone et al U.S. Pat. No. 3,900,975, issued Aug. 26, 1975 discloses a process for abrasively grinding copper in which the copper workpiece is cooled to a cryogenic temperature. The Elkins U.S. Pat. No. 4,447,952, issued May 15, 1984 describes an underwater cutting or penetrating device which uses a source of liquid nitrogen for cooling a workpiece before impact by an explosively driven member. The Bryne U.S. Pat. No. 3,712,306, issued Jan. 23, 1973 discloses a cryosurgical instrument which has an open ended chamber pressed into contact with tissue. A stream of liquified nitrogen impinges directly on the tissue which is to be necrotized by freezing. The Bettin U.S. Pat. No. 4,262,567, issued Apr. 21, 1981 and the Hagler U.S. Pat. No. 4,918,941, issued Apr. 24, 1990 disclose the use of cryogenic fluids for cooling microtomes.
A general object of this invention is to provide an improved method and apparatus for material removal by a high velocity stream impinging on the workpiece and to overcome certain disadvantages of the prior art.